Take your pick. Any $100 card will be better than internal graphics.
If you are looking for performance of a $200 card or better, you might want to consider upgrading your CPU to Core-i5 status. You have a Sandy Bridge motherboard, so you wouldn't need a new motherboard.
I agree. You need a better CPU (possibly even a new Power Supply) if you are going to get a $200+ card. If you're looking for a small boost in power, the Radeon HD 7750 is a good card, and won't put any strain on your Power Supply.